DESCRIPTION: This proposal is for continuation of ongoing studies on basolateral potassium channels investigated by the PI for many years. These basolateral potassium channels have been shown to be important in epithelial sodium absorption. The PI has identified ATP-regulated potassium channels present in the basolateral membrane of sodium-absorbing epithelial cells that may be responsible for the parallelism between the rate of sodium-potassium pump activity and the potassium conductance of the membrane. The current studies are focused on the potassium channels from the small intestinal cells of the salamander, Necturus maculosa. The application is divided into two phases which will be conducted simultaneously: first phase includes physiological and electrophysiological studies of the channels, while the second phase includes cloning and determining its structure-function relationships. The experimental approaches will include studies of single channel activity in basolateral membrane vesicles and classical microphysiological techniques. His first specific aim is designed to explore the effects of ATP, ADP and the ATP/ADP ratio on channel activity as well as to determine whether channel activity is affected by intracellular signals including phosphorylation/dephosphorylation mediated by protein kinases and/or phosphatases. The second specific aim focuses on testing further their model for "voltage gating" of the K(ATP) channels with specific reference to the mechanisms of action of the sulfonylurea derivatives and the "channel openers" such as diazoxide. The third specific aim will use conventional electrophysiological approaches to determine the extent to which the K(ATP) channels contribute to the total basolateral membrane conductance of the intact enterocyte and to the macroscopic pump-leak parallelism. The last specific aim will be directed at cloning the K(ATP) channel, determining its primary and putative secondary structure and initiating studies to determine its structure-function relationships. These studies are certainly important in our understanding of basic physiology related to potassium channels and their role in sodium absorbing epithelia.